Performing Sujud-ul-Sahw because of performing an additional Sujud and only being reminded of that after finishing Salah

Q: Shaykh `Abdullah bin `Abdul-`Aziz bin Khanin is the appointed Imam (the one who leads congregational Prayer) of Masjid (mosque) II in Bilsamar. He studied in the Halaqahs (learning circles) of Shaykhs Muhammad ibn Ibrahim and `Abdul-Latif (may Allah be merciful with them both). Being assigned in the year 1367 A.H., our concerned Imam was the first appointed Imam in the area of Ballasmar. Thanks to Allah, he has a sound `Aqidah (creed). The point is that while performing one Salah (Prayer), this Imam offered one extra Sajda (Prostration) out of forgetfulness. People told him about it after finishing Salah. The Imam then offered Sujud-ul-Sahw (Prostration of Forgetfulness). Nevertheless, some worshippers who had performed Salah with the Imam formed another congregation and repeated the same Salah. As this offended the Imam, we tried to reconcile between the two parties but the man who led the second congregation insisted that we refer the matter to your Eminence. It may be worth mentioning that the answer of `Ali ibn Nasir `Aly ibn Nasir implies vagueness when saying: Whoever leads another congregation. He said that people who prayed behind him were late comers i.e. they did not perform Salah with the first congregation. However, the Imam said that they were amongst worshippers who initially performed Salah behind him. `Ali ibn Nasir then commented that only two of those who initially performed Salah behind him prayed with the first congregation. Even so, the Imam asserted that all those who prayed with the second congregation had first prayed behind him. Of course, this caused a great deal of confusion. Moreover, this as well as other similar incidences negatively affect Ma'mums (those being led by an Imam in Prayer) causing them to doubt their Imams. Please advise! May Allah safeguard you!